1. Field of the Invention
This invention relates to an image holding member for electrophotography, having as the supporting drum a metal drum comprising one side face of the drum which is formed unitarily with the peripheral face of the drum, said metal drum having a rotatory supporting shaft formed integrally with the central portion of said side face.
2. Description of the Prior Art
Electrostatic images or toner images can be produced by various electrophotographic processes. And, the image holding members on which electrostatic images or toner images are formed may be classified into two groups of those having photoconductive layers called as the electrophotographic photosensitive members and those having no photoconductive layer.
An image forming member is generally constituted with a support and an image holding layer provided thereon.
Electrophotographic photosensitive members may have various constitutions in order to obtain desired characteristics depending on the kind of the electrophotographic process applied. As a typical example of electrophotographic photosensitive members, there have been widely used a photosensitive member having a photoconductive layer formed as the image holding layer on a support and a photosensitive member having lamination structure comprising a photosensitive layer and an insulating layer formed thereon as the image holding layer. The photosensitive member constituted with a support and a photoconductive layer is used for the most general electrophotographic process. That is, it is used for image formation by charging, image exposure and development, followed further by transfer, if desired. In the photosensitive member provided with an insulating layer, this layer is provided for various purposes such as protection of the photoconductive layer, improvement of the mechanical strength of the photosensitive member, improvement of dark decay characteristic or so as to be applied to a specific electrophotographic process. Typical examples of such photosensitive members having insulating layers or electrophotographic processes using the photosensitive members having insulating layers are disclosed in, for example, U.S. Pat. No. 2,860,048, Japanese Patent Publication No. 16429/1966, U.S. Pat. Nos. 3,146,145, 3,607,258, 3,666,363, 3,734,609, 3,457,070, and 3,124,456.
A certain electrophotographic process is applied on an electrophotographic photosensitive member to form an electrostatic image thereon, and the electrostatic image is developed to be visualized.
A typical constitution having no photoconductive layer has an insulating layer as the image holding layer. Typical processes using the image holding member of this type are mentioned below.
(1) A process as disclosed in Japanese Patent Publications Nos. 7115/1957, 8204/1957 and 1559/1968, for improving the durability of an electrophotographic photosensitive member against repetitive use, wherein development is carried out by transferring the electrostatic image formed on the electrophotographic photosensitive member onto an image holding member having no photoconductive member, followed by transfer of the toner image to a recording member.
(2) As another electrophotographic process for forming an electrostatic image on an image holding member having no photoconductive member corresponding to the electrostatic image formed on the electrophotographic photosensitive member, a process wherein an electrostatic image is formed by a certain electrophotographic process on a screen-shaped electrophotographic photosensitive member having numerous minute openings, corona charging treatment is performed through said electrostatic image on an image holding member having no photoconductive member thereby to form the electrostatic image on the image holding member having no photoconductive member through modulation of the ion streams of corona, which is then subjected to toner development and transferred onto a recording member to form the final image, as disclosed in U.S. Pat. Nos. 3,680,954, 3,645,614 and 4,255,507.
(3) According to still another electrophotographic process, a process wherein toner images formed on an electrophotographic photosensitive member or an image holding member having no photoconductive layer are transferred onto another image holding member having no photoconductive layer without directly transferring onto a recording member, and the transferring the images on the recording member, followed by fixing. This process is particularly effective for formation of color images or high speed copying. As a recording member, a flexible material such as paper or a film is generally used. For this reason, it is more effective for forming color images with accurate registration to transfer the tricolor images on an image holding member substantially free from deformation and to transfer the images at once on a recording member rather than to transferring the tricolor images while performing registration accurately. it is also effective for speed-up of copying that the toner images is transferred through the image holding member onto a recording member.
(4) As still another process, a process wherein electrical signals are applied on a multi-needle electrode to form electrostatic images corresponding to the electrical signals on the surface of an image holding member having no photoconductive layer, which are then developed to form images.
An image holding member to be used for electrophotography is liable to be damaged, because it is exposed to various electrical and mechanical shocks as by corona charging treatment, developing treatment, cleaning treatment and others. And, once an image holding member is damaged, the quality of the images formed is markedly lowered. Thus, it is a general practice to replace the image holding members with lowered performance with a good one. Accordingly, image holding members are also articles of consumption, and therefore they are required to be excellent in easiness of manufacture, cost, etc. Whereas, the element from the standpoint of manufacture and cost in the image holding members of the prior art, which has been deemed to be the most crucial problem, is the support. As the support, a metal drum is used as a general practice. Most of the metal drums employed are formed by casting a molten metal into a mold having an annular opening and then cooling the metal while the metal passes through said annular opening portion, namely according to the so called extrusion molding. However, a metal drum prepared by such a process, since it is prpared by drawing from a mold, has a thick wall to give a heavy metal drum. Also, the metal drum thus formed has none of both side faces, and therefore, in order to be mounted as the image holding member on the body of a copying device, flanges as the bonding members have to be separately formed and set up to both ends of the metal drum, and therefore a number of working steps are necessary for manufacture. As a metal drum which overcomes this problem, Japanese Laid-open Patent Application No. 159680/1981 proposes a metal drum in which one side face of the drum is formed integrally continuous to the peripheral face of the drum. However, for forming good images by rotating the image holding member within the electrophotographic apparatus, the fluctuation of rotating surface must be suppressed to 30.mu. or less. Whereas, the metal drum disclosed in the above laid-open patent application, due to the absence of a rotatory supporting shaft, the projection-recess portion for driving formed on the side face of the metal drum must be formed very precisely in order to permit the metal drum to rotate with high precision, and further the corresponding projection-recess portion for driving the metal drum must also be very precisely formed. However, it is not easy to form these projection-recess portions very precisely. Further, due to absence of a rotatory supporting shaft, the metal drum is required to be supported by these projection-recess portions, which should be in a shape of sufficient strength to function as the supporting section or to have a large thickness. Besides, generally speaking, in an electrophotographic apparatus, the metal drum needs to be conductive to the body of an electrophotographic machine. However, in the metal drum disclosed in the above laid-open patent application, due to absence of a rotatory supporting shaft, for conductive connection to the body of the electrophotographic machine, the driving and transmitting members for rotatory driving of the metal drum are required to be made all of a metal, whereby inconveniences occur in the use of parts of light-weight or low cost such as plastic gears, etc.